NAME

       gd_bof — find the start of data in a Dirfile field

SYNOPSIS

       #include <getdata.h>

       off_t gd_bof(DIRFILE *dirfile, const char *field_code);

DESCRIPTION

       The gd_bof() function queries a dirfile(5) database specified by dirfile and finds the beginning-of-field
       marker for the vector field given by field_code.

       The  caller  should  not assume that the beginning-of-field marker falls on a frame boundary.  The begin‐
       ning-of-field marker is never negative.

       For  a  RAW  field,  the  beginning-of-field  corresponds  to  the  frame  offset  of  that  field   (see
       gd_frameoffset(3)).  The beginning-of-field marker of the special field INDEX is zero.

       The  beginning-of-field  of  a  PHASE  field is the beginning-of-field of its input adjusted by the PHASE
       field's shift (or zero, if the shift would make it negative).  The beginning-of-field for all other  vec‐
       tor fields is the the latest beginning-of-field of any of its input fields.

       If  the  beginning-of-field  marker  of a field is greather than or equal to its end-of-field marker (see
       gd_eof(3)), then that field contains no data.  For a RAW field, the difference between the  locations  of
       the beginning- and end-of-field markers indicates the number of samples of data actually stored on disk.

       The dirfile argument must point to a valid DIRFILE object previously created by a call to gd_open(3).

RETURN VALUE

       Upon successful completion, gd_bof() returns a non-negative integer which is the sample number of the be‐
       ginning-of-field  marker  for  the  specified  field.  On error, it returns a negative-valued error code.
       Possible error codes are:

       GD_E_BAD_CODE
               The field specified by field_code or one of the fields it uses as input  was  not  found  in  the
               database.

       GD_E_BAD_DIRFILE
               The supplied dirfile was invalid.

       GD_E_DIMENSION
               A scalar field was found where a vector field was expected in the definition of field_code or one
               of its inputs, or else field_code itself specified a scalar field.

       GD_E_INTERNAL_ERROR
               An internal error occurred in the library while trying to perform the task.  This indicates a bug
               in the library.  Please report the incident to the GetData developers.

       GD_E_RECURSE_LEVEL
               Too  many  levels of recursion were encountered while trying to resolve field_code.  This usually
               indicates a circular dependency in field specification in the dirfile.

       The error code is also stored in the DIRFILE object and may be retrieved after this function  returns  by
       calling   gd_error(3).    A   descriptive  error  string  for  the  error  may  be  obtained  by  calling
       gd_error_string(3).

HISTORY

       The gd_bof() function appeared in GetData-0.7.0.

       Before GetData-0.10.0, this function could also fail with the error code GD_E_ALLOC.

       In GetData-0.10.0, the error return from this function changed from -1 to a negative-valued error code.

SEE ALSO

       gd_eof(3), gd_error(3), gd_error_string(3),  gd_frameoffset(3),  gd_open(3),  dirfile(5),  dirfile-encod‐
       ing(5)

Version 0.10.0                                  25 December 2016                                       gd_bof(3)